Dissolved Organic Carbon Retention in Soils

Interactions between dissolved organic C (DOC) and mineral soils were examined in a laboratory column study. Specific emphasis was given to comparisons of soil and solution measurements of organic C (OC) retention in four soil parent materials. Soil columns were leached with one of three concentrations of forest floor (FF) leachate or distilled water every third day for 1 yr. The concentration of DOC in solution was analyzed before and after percolation through soil columns to assess net release or retention of DOC. Changes in soil chemical properties (pH, loss‐on‐ignition [LOI], extractable Al and Fe) following leaching were consistent with podzolization. Micromorphological investigation of the soil materials following leaching showed increased accumulation of organo‐metallic coatings in materials treated with high concentrations of DOC relative to distilled water or low concentrations of DOC. The most dramatic changes in soil chemical properties were found in soils leached with high concentrations of DOC. Comparison of solution and soil measures of OC retention indicates that only ∼50% of the DOC lost from solution was measured as soil OC at the end of the experiment. This finding suggests that microbial decomposition is a significant factor regulating OC concentrations in soils and that soil solution data alone do not yield a complete picture of soil OC dynamics.